Elias Chatzitheodoridis, Sarah Haigh and Ian Lyon
Scanning electron microscope image of a mysterious oval structure in the Nakhla Mars meteorite.
Since NASA's Mars Science Laboratory (MSL) rover Curiosity landed on the red planet, each sol (a Martian "day") of the mission sees a flood of new photographs from Aeolis Palus -- the plain inside Gale Crater where Curiosity landed on Aug. 5. In September 2012, mission controllers sent the command for Curiosity to flip open the dust cap in front of the robotic arm-mounted Mars Hand Lens Imager (MAHLI). Until that point, the semi-transparent dust cap only allowed MAHLI to make out fuzzy shapes -- although it did a great job imaging Curiosity's "head" and it is also famous for capturing Curiosity's first color photograph. But since the true clarity of MAHLI has been unleashed, we've been treated to some of the most high-resolution views of the rover, Martian landscape and, most importantly, we've seen exactly what MAHLI was designed to do: Look closely at Mars rocks and dirt, assembling geological evidence of potential past habitability of Mars.
The Business End
Curiosity is armed with 17 cameras and MAHLI is designed to capture close-up photos of geological samples and formations as the rover explores. MAHLI was designed and built by Malin Space Science Systems and is analogous to a geologist's hand lens -- only a lot more sophisticated. Its high-resolution system can focus and magnify objects as small as 12.5 micrometers (that's smaller than the width of a human hair!). This photograph captured by the rover's Mastcam shows the MAHLI lens (with dust cap in place) in the center of the end of Curiosity's instrument-laden robotic arm.
To aid its studies, MAHLI is equipped with four LEDs to light up the imager's samples.
The first photograph to be returned from MAHLI without the dust cover in place was received on Sol 33 (Sept. 8) of Curiosity's mission. Shown here is a view of the ground immediately in front of the rover. Although this photo was a test, mission scientists were able to do a very preliminary study of the large "pebble" at the bottom of the picture: "Notice that the ground immediately around that pebble has less dust visible (more gravel exposed) than in other parts of the image. The presence of the pebble may have affected the wind in a way that preferentially removes dust from the surface around it," they wrote.
How Did Lincoln Help MAHLI?
On Sol 34 (Sept. 9), MAHLI was aimed at Curiosity's calibration target. This target is intended to color balance the instrument and provide a "standard" for mission scientists to refer to. The 1909 Lincoln penny was provided by MAHLI's principal investigatory Ken Edgett. Using a penny as a calibration target is a nod to geologists' tradition of placing a coin or some other object of known scale as a size reference in close-up photographs of rocks, says the MSL mission site.
Although MAHLI will be used to examine microscopic scales, it is showing its prowess at generating some spectacular high-definition views of the rover. Shown here is a mosaic of Curiosity's three left-side dusty wheels.
Hazard Avoidance Cameras
Hazard Avoidance Cameras, or Hazcams, have become "standard issue" for the last three rovers to land on Mars. Mounted on the front and back of rovers Opportunity, Spirit and Curiosity, these small cameras provide invaluable information about the terrain and potential hazards surrounding the rovers. These cameras are not scientific cameras -- they are engineering cameras. Shown here, MAHLI has imaged the four front Hazcams on Curiosity. Interestingly, it was these cameras who returned Curiosity's first dusty image after touch down in August.
Using the flexibility of the robotic arm, MAHLI was able to check the underside of Curiosity. As the camera can focus on objects from 0.8 inch (2.1 centimeters) to infinity, MAHLI has incredible versatility allowing mission controllers to focus on the very small features of Mars to checking the health of the rover to viewing the impressive vistas beyond.
In October 2012, the Internet was abuzz with speculation about a "mystery object" lying beneath the rover during digging operations at "Rocknest." Sadly, after studying the translucent object, mission scientists deduced that it wasn't anything native to the alien environment, it was actually a piece of plastic that had fallen from Curiosity. Yes, Curiosity is littering the red planet.
The MAHLI camera was very attentive while Curiosity dug trenches in the Mars soil at "Rocknest."
In early 2013, MAHLI snapped another curious photo. This time, after driving to a rocky outcrop at a location dubbed "Yellowknife," the camera picked out what appeared to be some kind of organic-looking object embedded in the rock. Nope, it's not a Mars "flower" -- more likely it's a concentration of minerals.
In what has become an iconic photo of Curiosity, MAHLI was commanded to capture dozens of high-resolution pictures of the rover. Like an "arms length" shot you may have in your Facebook profile, Curiosity did the same, composing a mosaic of pics taken with its outstretched robotic arm.
Curiosity Cleans Up!
The Mars rover isn't only a scientific superstar, it also has a talent for cleaning. This circular pattern on a Mars rock was brushed aside by Curiosity's Dust Removal Tool (DRT), helping the rover carry out analysis of the rock surface beneath the layer of dirt.
Scientists have found a strange structure resembling a microbial cell inside a Martian meteorite, but they're not claiming that it's evidence of Red Planet life.
The researchers discovered the microscopic oval object within the Nakhla Mars meteorite, which fell to Earth in Egypt in 1911. While the structure's appearance is intriguing, it most likely formed as a result of geological rather than biological processes, team members said.
"The consideration of possible biotic scenarios for the origin of the ovoid structure in Nakhla currently lacks any sort of compelling evidence," the scientists write in a new study published this month in the journal Astrobiology. "Therefore, based on the available data that we have obtained on the nature of this conspicuous ovoid structure in Nakhla, we conclude that the most reasonable explanation for its origin is that it formed through abiotic processes." [The Search for Life on Mars (A Photo Timeline)]
A Cell-like Structure
The hollow ovoid is about 80 microns long by 60 microns wide, researchers said — far larger than most terrestrial bacteria but in the normal size range for eukaryotic Earth microbes (single-celled organisms that possess nuclei and other membrane-bound interior "organelles"). The study team is confident that the object is native to the sample and not the result of terrestrial contamination.
The scientists studied the structure using a number of different techniques, including electron microscopy, X-ray analysis and mass spectrometry. This work revealed that the ovoid is composed of iron-rich clay and contains a number of other minerals.
The researchers run through a number of possible formation scenarios in the new study, eventually concluding that the ovoid most likely formed when materials partially filled in a pre-existing vesicle — a vapor bubble, for example — in the rock.
But this supposition doesn't rule out the possibility that Martian lifeforms had something to do with the structure, team members said.
"Despite the extremely biomorphic overall shape of the ovoid, it is highly unlikely that it itself was an organism," said lead author Elias Chatzitheodoridis, of the National Technical University of Athens in Greece.
"However, it could have been formed directly by micro-organisms, or it could trap organic material that came from elsewhere," Chatzitheodoridis told Space.com via email. "That the ovoid is hollow means that there is enough space to accommodate colonies of microorganisms."
Making a firm link to Mars life would require further study and further discoveries, he added.
"We would be happy if we could have found more than one ovoid, with exactly the same texture both in the micro and the nanoscale," Chatzitheodoridis said. "However, we require to open up enough sample in a very careful way. Compelling evidence, though, would be if we could really find many of the same, clearly in a form of a colony, together with chemical and mineralogical biosignatures that are common for terrestrial microbes."
Nakhla is a well-studied meteorite — scientists have spotted possible signs of Mars life within it before —and previous research has mapped out its history in some detail. Nakhla's parent rock apparently crystallized about 1.3 billion years ago, Chatzitheodoridis and his colleagues write in the new study, then experienced two shock events that heated it up considerably.
The first of these shocks likely occurred around 910 million years ago and the second 620 million years ago. This latter event, which was triggered by a nearby meteorite strike on Mars, apparently included the flow of hot water through Nakhla's parent outcrop, the authors write. Finally, about 10 million years ago, another impact blasted Nakhla free of Mars, sending it on a looping trip through space that ended with its arrival at Earth in 1911.
Whether or not the Nakhla ovoid has some connection to Martian life, study of the meteorite can help researchers better understand the Red Planet's past (and, perhaps, present) potential to support life, Chatzitheodoridis said.
Martian meteorites contain "important information, and latest work has shown that now one has to look more carefully at them and in finer detail," he told Space.com.
"In our case, it is such work that allowed us to see from a small volume of sample a big story, i.e., that hydrothermal waters have actually acted also in the latest periods of Martian history, even if they were caused by a bolide impact, and that they were capable of initiating a number of complicated processes that resulted in the formation of niche environments which can sustain life, if life emerged on the planet," Chatzitheodoridis added.
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